Somnambulism (sleepwalking) Is a Parasomnia Characterized by Behavioral Manifestations of Various Degrees of Complexity

SOMNAMBULISM (SLEEPWALKING) IS A PARASOMNIA CHARACTERIZED BY BEHAVIORAL MANIFESTATIONS OF VARIOUS DEGREES OF COMPLEXITY AND duration occurring during non-rapid eye movement (NREM) sleep.1 Somnambulistic episodes generally arise from sudden but incomplete arousal from slow-wave sleep (SWS; stage 3 and 4 sleep) during the first third of the night2-4 but may also occur out of stage 2 sleep or later during the night.5-7 Somnambulism is considered to be a “disorder of arousal,”4,8 as affected individuals appear to be caught between NREM sleep and full awakening. One of the more controversial findings regarding the sleep electroencephalogram (EEG) of somnambulistic patients is the presence of hypersynchronous delta activity (HSD), usually described as continuous high-voltage (> 150-uV) delta waves occurring during SWS or immediately prior to an episode. This activity was first noted prior to sleepwalking events by Jacobson et al.2 Subsequent studies in adult parasomniacs have yielded mixed results, with sleepwalking or sleep terror episodes being occasionally,5,9 often,10 or always11,12 associated with HSD. These inconsistencies may be due in part to the age and clinical history of the patients13,14 and methodologic differences in the identification and quantification of HSD.15-17 Schenck et al,17 for example, found that most behavioral and nonbehavioral arousals from SWS in adult patients were not preceded by a delta-wave build-up and that only 15.5% were preceded by delta-wave clusters, but no comparisons were made with more-traditional definitions of HSD. More recently, 1 investigation found that the frequency of HSD in the EEG of adult sleepwalkers was dependent on the derivation investigated (presence of a frontocentral gradient).15 To help resolve this controversy and fill the void in knowledge concerning the specificity and sensitivity of HSD for somnambulism, the present study used the polysomnographic data collected by Joncas et al7 to systematically evaluate HSD during the NREM sleep of somnambulistic patients and controls recorded during normal sleep and following 38 hours of sleep deprivation (a condition known to increase the frequency of somnambulistic episodes recorded in the laboratory). Specifically, differences in the occurrence of HSD were investigated over 5 different derivations (F3, C3, P3, T3, and O1) throughout participants’ NREM sleep (stage 2, 3, 4) and immediately prior to somnambulistic episodes. HSD was assessed with several variables, including the most frequently described methods,11,13 and with Schenck et al’s17 criteria for delta-wave build-up and delta-wave clusters. It was hypothesized that sleepwalkers would have more HSD than control subjects and that HSD would increase during recovery sleep following a fronto-occipital gradient. Secondary goals were to investigate the temporal and topographic distribution of HSD prior to somnambulistic episodes and to assess HSD prior to somnambulistic behaviors as a function of episode complexity. Hypersynchronous Delta Waves and Somnambulism: Brain Topography and Effect of Sleep Deprivation